CHUNK #3: Writing Surface — editor wiring, storage view, polish

Complete the Writing Surface chunk: wire the web writing view to the
offline-first storage adapter, finish the editor package exports, and
apply Step 4 polish (SVG monogram logo, real project in the sidebar,
font settings → CSS variables).

Editor package
- Re-export EditorContent + Editor type from @pubscript/editor so the
  web app never imports TipTap directly.

Web writing view (apps/web)
- project-store (zustand) over storageLocal: project, chapters, active
  chapter, autosave via createAutosave, idle detection via
  createIdleDetector.
- Client-side seed mirroring the server seed ("The Glass Harbor").
- WritingView component: editor + autosave label + word/scene count +
  chapter nav; wire the /write route inside AppShell.
- Import editor.css in main.tsx.

Core storage contract
- Extend StorageAdapter with createBook/listBooks/listChapters;
  implement in local + server adapters; update contract test mock.

Polish
- Sidebar: SVG monogram logo + live project title/word count instead
  of the placeholder "The Silent Cartographer".
- Fonts: applyFontSettings() in the theme engine writes --ps-font-*
  variables; .ps-content reads --ps-font-size/leading/measure; settings
  store applies fontSize on boot and change.

Docs
- PLAN.md: CHUNK #3 → in progress.
- CHUNK#3_PROGRESS.md: steps 1–3 done, step 4 polish in progress.

Verified: full workspace typecheck clean, lint clean, core 24 / ui 5 /
editor 7 tests pass, web build clean. (server vitest hits EADDRINUSE on
8080 — pre-existing Docker WordPress port conflict, unrelated.)

packages/ui/src/AppShell.css

@@ -118,12 +118,12 @@ body {
   overflow: auto;
 }
 .ps-content {
-  max-width: 820px;
+  max-width: var(--ps-font-measure, 720px);
   margin: 0 auto;
   padding: 32px 24px 96px;
   font-family: var(--ps-font-body);
-  font-size: 17px;
-  line-height: 1.75;
+  font-size: var(--ps-font-size, 17px);
+  line-height: var(--ps-font-leading, 1.75);
 }
 
 /* ---- Sidebar nav ---- */
@@ -137,7 +137,12 @@ body {
   align-items: center;
   gap: 8px;
 }
-.ps-logo .ps-logo-mark { color: var(--ps-accent); }
+.ps-logo .ps-logo-mark {
+  color: var(--ps-accent);
+  width: 1.35em;
+  height: 1.35em;
+  flex: none;
+}
 .ps-nav-section-title {
   font-size: 11px;
   text-transform: uppercase;

packages/ui/src/theme.ts

@@ -130,3 +130,39 @@ export function applyTheme(id: ThemeId): ThemeId {
 export function getActiveTheme(): ThemeId {
   return activeTheme;
 }
+
+/**
+ * Runtime font overrides for the writing surface. See PLAN.md §4.1/§4.7.
+ * These layer on top of the theme's base font families.
+ */
+export interface FontSettings {
+  /** Body font family override (falls back to the theme's body font). */
+  family: string;
+  /** Base body font size in px. */
+  size: number;
+  /** Line height as a unitless multiplier. */
+  leading: number;
+  /** Prose column max width (measure) in px. */
+  measure: number;
+}
+
+export const DEFAULT_FONT_SETTINGS: FontSettings = {
+  family: "",
+  size: 18,
+  leading: 1.7,
+  measure: 720,
+};
+
+/**
+ * Apply font settings by writing CSS variables to :root. The prose column
+ * (`.ps-content`) reads these; an empty `family` leaves the theme's body font
+ * in place. Safe to call before the DOM exists (no-op).
+ */
+export function applyFontSettings(s: Partial<FontSettings>): void {
+  const root = typeof document !== "undefined" ? document.documentElement : undefined;
+  if (!root) return;
+  if (s.size != null) root.style.setProperty("--ps-font-size", `${s.size}px`);
+  if (s.leading != null) root.style.setProperty("--ps-font-leading", String(s.leading));
+  if (s.measure != null) root.style.setProperty("--ps-font-measure", `${s.measure}px`);
+  if (s.family != null && s.family !== "") root.style.setProperty("--ps-font-body", s.family);
+}